A recent mission atop a Hawaiian volcano shows humans still have much to learn before they set foot on another world.

The drive to the little white dome on the northern slope of Mauna Loa is a bumpy one. Mauna Loa, the “Long Mountain,” is a colossal volcano that covers half of the island of Hawaii. The rocky terrain, rusty brown and deep red, crunches beneath car tires and jostles passengers. Up there, more than 8,000 feet above sea level and many miles away from the sounds of civilization, it doesn’t feel like Earth. It feels like another planet. Like Mars.

For the last five years, small groups of people have made this drive and moved into the dome, known as a habitat. Their job is to pretend that they really are on Mars, and then spend months living like it. The goal, for the researchers who send them there, is to figure out how human beings would do on a mission to the real thing.

In February of this year, the latest batch of pioneers, a crew of four, made the journey up the mountain. They settled in for an eight-month stay. Four days later, one of them was taken away on a stretcher and hospitalized.

The remaining crew members were evacuated by mission support. All four eventually returned to the habitat, not to continue their mission, but to pack up their stuff. Their simulation was over for good. The little white dome has remained empty since, and the University of Hawaii, which runs the program, and NASA, which funds it, are investigating the incident that derailed the mission.